BSI Image Sensor Reflective Structure for Long-Wavelength Light
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Solution Overview
Problem
Backside illumination (BSI) image sensors lose light with large wavelengths as it is absorbed by the back-end-of-line (BEOL) interconnect structure, resulting in reduced light quantum efficiency.
Innovation Solution
A reflective structure formed by front-end-of-line (FEOL) manufacturing operations is introduced to reflect light back into the image sensors, reducing light entry into the BEOL interconnect structure and enhancing light quantum efficiency for longer wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reflective structure is added to improve light quantum efficiency for large-wavelength light, then light quantum efficiency is improved, but device complexity increases
Solution Approach 1:
The reflective structure is merged with the existing gate structure of the transistor, using the same conductive material (polysilicon or metal) and forming both structures simultaneously during the same fabrication process steps. This integration eliminates the need for separate reflective structure fabrication, reducing process complexity while maintaining the light reflection function that improves quantum efficiency for large-wavelength light.
Solution Approach 2:
The gate structure serves dual functions: electrical control of the transistor and optical reflection for improving light quantum efficiency. By making the gate structure also function as the reflective structure, the patent eliminates redundant components and simplifies the overall device architecture while achieving improved performance for large-wavelength light detection.
2Reliability
If the reflective structure is formed separately from the gate structure, then light reflection is improved, but manufacturing process complexity increases
Solution Approach 1:
The reflective structure and gate structure are formed as integrated components using the same fabrication processes. The gate dielectric layer, gate conductive layer, and spacer formation steps create both structures simultaneously, eliminating separate manufacturing steps and simplifying the overall fabrication process while maintaining effective light reflection.
Solution Approach 2:
The reflective structure is formed preliminarily during the standard transistor fabrication process before final device assembly. By incorporating the reflective function into the gate structure formation steps, the patent ensures light reflection capability is established early in the manufacturing process without requiring additional post-processing steps.
3Reliability
If the reflective structure uses different material than gate structure, then optical performance is optimized, but material complexity and fabrication difficulty increase
Solution Approach 1:
The reflective structure uses the same conductive material as the gate structure (polysilicon or metal), ensuring material homogeneity throughout the device. This approach simplifies fabrication by using identical material deposition and processing steps for both structures, while the reflective performance is optimized through proper structural design and positioning rather than material variation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The reflective structure improves light quantum efficiency for large-wavelength light and simplifies the design and manufacturing of the BEOL metallization structure, while providing process flexibility and maintaining high efficiency.
Implementation Method 1
A reflective structure is formed using front-end-of-line (FEOL) manufacturing operations to reflect light back into the image sensors
Data Source
AI summary
A semiconductor image sensing structure includes a semiconductor substrate having a front side and a back side, a pixel sensor disposed in the semiconductor substrate, a transistor disposed over the front side of the semiconductor substrate, and a reflective structure disposed over the front side of the semiconductor substrate. A gate structure of the transistor and the reflective structure include a same material. A top surface of the gate structure of the transistor and a top surface of the reflective structure are aligned with each other.